/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Restartless.
 *
 * The Initial Developer of the Original Code is The Mozilla Foundation.
 * Portions created by the Initial Developer are Copyright (C) 2010
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Edward Lee <edilee@mozilla.com>
 *   William Elwood <we9@kent.ac.uk>
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK *****
 */

'use strict';

/**
 * Save callbacks to run when unloading. Optionally scope the callback to a
 * container, e.g., window. Provide a way to run all the callbacks.
 *
 * @usage unload(): Run all callbacks and release them.
 *
 * @usage unload(callback): Add a callback to run on unload.
 * @param callback <function>  0-parameter function to call on unload.
 * @return <function>  A 0-parameter function that undoes adding the callback.
 *
 * @usage unload(callback, container): Add a scoped callback to run on unload.
 * @param callback <function>  0-parameter function to call on unload.
 * @param container <node>  Remove the callback when this container unloads.
 * @return <function>  A 0-parameter function that undoes adding the callback.
 */
function unload(callback, container) {
    // Initialize the array of unloaders on the first usage
    var unloaders = unload.unloaders;
    if (unloaders == null)
        unloaders = unload.unloaders = [];

    // Calling with no arguments runs all the unloader callbacks
    if (callback == null) {
        unloaders.slice().forEach(function(unloader) {
            unloader()
        });
        unloaders.length = 0;
        return undefined;
    }

    // The callback is bound to the lifetime of the container if we have one
    if (container != null) {
        // Remove the unloader when the container unloads
        container.addEventListener("unload", removeUnloader, false);

        // Wrap the callback to additionally remove the unload listener
        var origCallback = callback;
        callback = function() {
            container.removeEventListener("unload", removeUnloader, false);
            origCallback();
        }
    }

    // Wrap the callback in a function that ignores failures
    function unloader() {
        try {
            callback();
        } catch(ex) {}
    }
    unloaders.push(unloader);

    // Provide a way to remove the unloader
    function removeUnloader() {
        var index = unloaders.indexOf(unloader);
        if (index != -1)
            unloaders.splice(index, 1);
    }
    return removeUnloader;
}
